What would be the mass of a bag of anhydrous magnesium sulfate, MgSO4, if it contained the same amount of magnesium as a 1.00 kg bag of Epsom salts, MgSO4 * 7H2O? Give your answer in grams.

Answer 1

There are long ways and short ways to do this but the best way is to use something called the chemical factor. That isn't taught in chemistry courses anymore. The chemical factor has gone the way of normality of solutions; that isn't taught anymore either. Shame. mm will stand for molar mass. am stands for atomic mass.

1,000g MgSO4.7H2O x (am Mg/MgSO4.7H2O) x (mm MgSO4/am Mg) = ?
You see the first factor convert from grams MgSO4.7H2O to grams Mg while the second factor converts from Mg to MgSO4. Obviously the atomic mass of Mg cancels so you need only one factor which is
1,000 g MgSO4.7H2O x (mm MgSO4/mm MgSO4.7H2O) = ? g MgSO4.
Most schools now teach this type problem by calculating the percent MgSO4 in MgSO4.7H2O and changing that to 1000 g sample instead of a 100 g sample. Post your work if you get stuck.